The present invention relates to a flow distribution mixer distributing the inlet flow into a plurality of flow channels and then combining the partial flows from the plurality of flow channels to the outlet flow, in particular for high performance liquid chromatography application.
In high performance liquid chromatography (HPLC), a liquid has to be provided usually at a very well controlled flow rate (e.g. in the range of microliters to milliliters per minute), at a very well controlled composition (e.g. in the range of 0.3% or better) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid containing compounds to be separated is driven through a stationary phase (e.g. contained in a chromatographic column), thus separating different compounds of the sample which may then be identified.
The mobile phase, for example, a solvent, is pumped under high pressure typically through a column filled with packing material, and the sample (e.g. a chemical or biological mixture) to be analyzed is injected into the stream of the mobile phase and with that is transported to the column. As the sample passes through the column driven by the liquid flow, the different compounds, each one having a different affinity for the packing medium, move through the column with different velocities. Those compounds having higher affinity to the stationary phase (e.g. a packing medium) move more slowly through the column than those having lower affinity, and this velocity differences results in the compounds being separated from one another as they pass through the column.
During operation, a flow of the mobile phase, typically driven by a high pressure chromatographic pump, traverses the column filled with the stationary phase, and due to the interactions between the mobile, the stationary phase and sample components a separation of different compounds may be achieved. As a result of flow passing through the stationary phase and depending on the physical properties of the stationary phase and the mobile phase, a relatively high pressure drop takes place along the column. The composition of the mobile phase is in many cases controlled by the pump operation, as the pump blends single flows of mobile phase constituents according to the pump settings or program. These flows are then combined together to provide a mixed flow of the mobile phase or eluent. The composition and the flow rate of the mobile phase are usually precisely controlled.
The fluctuations of the mixing ratio in an eluent flow generated e.g. by an HPLC pump can lead to undesired base line noise, bad reproducibility of the analysis or to separation performance deterioration. For certain applications, e.g. separations using eluents with UV-absorbing additives, the strict requirements to the constancy or smoothness of the eluent composition over the separation time cannot be satisfied without using additional mixing appliances which disperse the zones with fluctuations of the eluent composition.
U.S. Pat. No. 6,629,775 B2, by the same applicant, discloses a mixing apparatus wherein a fluid is progressing from an inlet tubing to an outlet tubing. Every segment of the liquid is part by part transferred to the outlet channel via numerous restrictor channels. The distances between the restrictor channels determine a dispersion pattern for any segment of the flow, progressing from the inlet chamber in the form of a reservoir channel to the outlet. The nearer the outlet channels are placed one to another, the higher is the permeability to the outlet collector at the respective location. Delaying partial flows of the fluid with different flow delays and providing different flow volumes for the partial flows results in a predetermined flow distribution function thus determining a dispersion pattern. This allows for a continuous dispersion of a fluid property which is intended to be mixed, for instance to be homogenized, in accordance with a predefined fluid distribution function.